Finish-grinding and polishing stones



Patented Dec. 22, 1942 UNITED STATES PArENr orifice FINISH-GRINDING AND POLISHI'NGSTONES Ernest P. Ma's, Chicago, 111.1

No Drawing.

7 Claims.

in use, which will not cause the air in the grinding room to be vitiated by abrasive dust and metal dust, and which will produce an exceedingly highly polished surface having no residual scratches.

, In one of its immediate commercial objects. my invention particularly aims to an artificial stone of this class for use in preparing the tubular-cylindrical copper cylinder of a rotogravure printing press for its intaglio-etching, which stone will accomplish the complete finishing of such a cylinder far more speedily, cheaply and eifectively than the formerly customary preparation of such a cylinder. Being initially of a nonuniform and oversized diameter, ach such cylinder heretofore required three consecutive finishing operations: First, a rough grinding with a rather coarse abrasive stone for giving the cylinder a uniform diameter slightly larger than that needed for the finished cylinder; next, a finish-grinding and polishing to reduce the cylinder to the proper size and to give it a smooth surface; and then a manual after-polishing (with emery paper and rouge cloth for eliminating the invariably present residual scratches.

The successive introduction (in 1925) of the artificial stone of my U. S. Patent No. 1,718,827 and of the finish-grinding stone of my (later filed) Patent No. 1,658,248 reduced the time needed for the second of the said three steps, and also lessened the residual scratches so as to reduce the time needed for the manual afterfinisning, thereby reducing the total time for finishing a cylinder (of the size used for printing photogravure supplements of newspapers) from the initially needed 7 hours to the still undesirably long total of 3 /2 to 4 hours. However, these patented stones did not afiect either the initial rough grinding or the manual after-polishing, each of which vitiated the air by abrasive and copper particles so as to require an air exhaust installation for protecting the health of the cylinder grinders. More recently, the use of thin- Application November 12, 1940, V Serial No. 365,325

ner and hence less expensive cylinders has also 7 made it highly desirable to diminish the diameter-reduction by the initial rough grinding, and

the use of much finer screened etchings now requires the elimination of even: extremely fine surface scratches (so-called lines) which were hard to see on the only moderately polished surfaces of the cylinders.

Consequently, users of photogravure presses have long felt the need of cylinder-finishin means which would further reduce the total required time, which would completely eliminate residual scratches and the corresponding afterfinishing, and which would give the cylinder such a high and mirroring polish that the finisher could readily detect even minute'imperfections such as might have been caused by impurities floating in the air. 4

In planning to meet this need I first studied out the heretofore apparently unknown reasons why the heretofore customary three-step procedure required such a long total time, why the second of these steps invariably left considerable residual scratches requiring the later manual after-polishing, and why the entire procedure failed to produce a polished surface for readily disclosing possibly still remainingminute scratches. This study disclosed:

(1) That the heretofore used main abrasives were so much harder than copper, usually sharpedged and of such large granules (even when sifted through a 300 mesh per inch screen) as to cut undesirably deep furrowsand to detach sharp-edged particles or slivers of copper, which thereafter would scrape on the surface of the cylinder to produce new scratches or enlarge already existing ones. Also, that with even 'crocus used in so large a proportion to the body material of the stone, as with that of my Patent No. 1,658,248, the resulting scratches could not be adequately eliminated by other'ingredients of the stone.

(2) That the deleterious scraping of already detached copper particles would be increased if the body of the stone was not readily softened uniformly at its face by the grinding water, as with both of my previous stones, since any'hard detached stone portions then pressed unduly on these copper particles. v I

(3) That the sharp-cutting and scraping "action of the heretofore used abrasives could not adequately be mollified by the polishing ingredients used with them, because the abrasive particles were usually too hard to be crushed or even dulled at their edges.

(4) And that no heretofore used stone included any ingredients which could produce the needed mirroring finish, and which wouldprevent degrees to harden the stone in about'12 hours.

tached copper particles from scraping on the cylinder and deter their cutting into already existing scratches.

To utilize my knowledge of the just listed reasons, I then experimentally determined how to improve the body of the stone, studied the relative desirability of different abrasives and of ingredients for mollifying their cutting action, found ingredients which during the operation of the stone would form a continuously renewing coating on which detached copper particles would he slid from under the stone by the moving muck, and included ingredients which impart a highly mirroring surface to the cylinder. Then I experimentally determined the proportioning. of such selected ingredients and a method of manufacturing the here disclosed new stones for completely meeting the previously recited long felt need. Typical of ingredients which I have found to blend and cooperate suitably in the hereafter recited proportions, I used:

As the body material of the stone, 2. litharge cement'consisting of a yellow -or orange-yellow lead monoxide bonded by sugared glycerine somewhat diluted with enough water to compensate for the use of a monoxide harder than the formerly used sulphur colored'one;

As the abrasive, a natural emery only slightly harder than copper, soft enough to be crushed during the grinding, and obtainable in extremely fine form, such as lightest particles separated from Turkish emery by air flotation;

For softening the cutting of the abrasive, Glassite '(black rouge) which partly cuts and partly polishes copper; and

As polishers and polish Spreaders, marine diatomaceous (infusorial) earth (a siliceous residue of algae), bone charcoal which also is easily crushed and spreads out the diatomaceous earth, and oxalic acid which, together with the charcoal and the diatomaceous earth will produce a highly mirroring polish.

Illustrative of a suitable 'proportioning of these ingredients and of a quite satisfactory procedure for making a batch of six twelve-pound stones of a disk-shape 8 inches indiameter and 3 inches thick, to be rotated at 450 to 5001B. P. M. I may start with 608 ounces lead monoxide, 320 oz. Turkish emery,

8 oz. London rouge, 10oz. glassite, 6 oz. oxalic acid, 8 oz. marine diatomacea, 4 oz. bone charcoal, 9 quarts glycerine, .9 quart water, and 13' oz. brown sugar.

In preparing such a batch of the stones, I first thoroughly intermingle the lead monoxide, em-

ery, rouge, glassite, oxalic acid, diatomacea and bone charcoal (all dry) and force the resulting mixture through a screen of not less than 300 and preferably 3'75 mesh per inch. This not only screens out larger particles and breaks up any lumps, but also finely cuts up the fluffy diatomacea and charcoal which could not readily be sifted if not mingled with the other ingremix-'this" solution with the previously intermingled dry ingredients to form the resulting syrupy mixture into interiorly greased molds in a room at a temperature of about 70 degrees, which may be raised later on to'about SO-de- With a disk-shaped stone of this consistency rotated at 400 to 500 R. P. M., or about twice the speed of the formerly used finish-grinding stones, and with water fed between a flat face of the stone and a copper cylinder, the increased speed compensates for the much minute size of the abrasive particles. So also, these emery particles are somewhat crushed even under the lighter pressure needed with my new stone, and the two rouges soften the action of the emery, the grinding shaves only extremely minute particles off the cylinder.

During the use of the stone the released particles of charcoal and diatomaceous earth intermingle with oxalic acid and grinding water to form a polishing paste, part of which temporarily adheres to thesurface of the cylinder and this continually renewed coating presents a slippery face on which detached copper particles can readily slide from under the stone. Moreover,

some of this paste also fills into scratches on the cylinder-to deter suchdetached particles from cutting into or enlarging those scratches. Consequently, when the pressure on the stone is gradually decreased after the cylinder has been groundalmost down to the needed diameter, even the greatly reduced scratchesproduced by the more minute abrasive particles gradually dis-- appear entirely. Then, when the supply of grinding water is increased, the charcoal in the paste enables the oxalic acid to produce its highly mirroring effect, and a further increase of this water supply'later on rinses the residual paste off the cylinder.

When'thus used my new stones have already proven in large rotogravure printing plants, such as that of the Chicago Tribune, to require only from 2 to 3 hours for the total cylinder preparation time of a'cylinder of the now used hardness of copper Moreover; the composition of such stones can readily be varied according to suit different hardnesses of the cylinders, as, for example, by varying the proportion of the lead and monoxide to the-glycerine, or for use in finishing other metals. Indeed, stones of the heretofore detailed composition are being used with satisfaction for the finish-polishing (or lapping) of steel cylinders used in printing on waxed paper, and smaller (usually rectangular stones) for manualuse on small'copper cylinders used for printing on textiles.

I claim as my invention:

1. An artificial grinding :and polishing stone for finishing the S111f3CeLOf. a metal, which has a non-abrasive cementitious body comprising leadmonoxide, glycerine, and water adapted to 'have its face portion ground-into small particles during the grinding tdform a much with water .used during the. grinding, and in which oommi nuted particles'ofabrasivafsmoothing and polishing materials are i'mbedded; characterized by imbedded abrasive particles of natural emery and rouge only slightly. harder than the said metal, and: the smoothing and polishing materials including a'plurality of ingredients such as infuso-rial earth, bone charcoal and oxalic acid, adapted, conjointly with water used during the grinding, to: constitute a polishing paste adapted to fill cracks on the surface of themetal and to form' a continuallyurenewing coatingon the said surface. to prevent already detached metal particles from-bein forcibly pressed against the saidsurface while these particles are being moved out from under stone: by the said muck and water.

2. A metal-grinding and polishing stone as per claim 1, in which the said comminuted ingredients include a charcoal which is uniformly fine and crushable, and uniformly crushable infusorial earth sufficient in quantity to intermingle fully with the charcoal, to carry abrasive particles released from the stone to the metal and for enabling the intermingled charcoal and infusorial earth to prevent the abrasive particles from cutting deeply into the metal.

3. A grinding and polishing stone as per claim 1, in which the oxalic acid of said plurality of ingredients for smoothing and polishing is present in a sufiicient quantity for producing a highly mirroring surface on the metal to be polished when the grinding pressure is relaxed and the supply of grinding water is increased.

4. A grinding and polishing stone as per claim 1, in which the abrasive particles of natural emery and rouge are sufiiciently soft to be somewhat crushed during the grinding operation, and in which the particles imbedded in the stone also include black rouge (glassite) which will partly abrade and partly polish the metal on which the stone is to be used.

5. An artificial stone composition for wetgrinding and polishing copper, comprising the product resulting from the hardening of a thoroughly intermingled mixture of the following ingredients in approximately their recited proportions: 608 ounces yellow or orange-yellow lead monoxide, 320 ounces air-floated natural emery, 8 ounces London rouge, 10 ounces black rouge, 6 ounces oxalic acid, 8 ounces marine diatomacea,

8 ounces bone charcoal, 9 quarts glycerine, 13 ounces brown sugar and nine-tenths of a quart of water.

6. A stone for use with water or the like in grinding and polishing a. metal such as copper, comprising a litharge cement body including glycerine and Water; finely comminuted particles of air-floated natural emery, red and black rouge, distributed therein, and of a total weight approximately half the weight of the litharge cement; and a plurality of smoothing and polishing ingredients including infusorial earth, bone charcoal, and oxalic acid, also distributed in the cement body in finely divided form, the total weight of the last named ingredients being about ten per cent of the weight of the emery.

7. A stone for wet-grinding and polishing copper, comprising a hard but water-softenable cement body including lead monoxide, glycerine and water, softer than copper and uniformly impregnated with finely comminuted ingredients; the said ingredients of emery and rouge comprising a natural emery only slightly harder than copper, in particles siftable through a screen of about 600 meshes per inch, and with the weight of the emery constituting less than one-third the weight of the stone; the ingredients also including finely distributed metal-polishing ingredients including diatomaceous earth, bone charcoal, and oxalic acid in particles siftable through a 300 mesh screen, and jointly weighing not more than about 12 per cent as much as emery.

ERNEST P. lVIARS. 

